Trunked RF repeater systems have become a mainstay of modern RF communications systems, and are used, for example, by public service organizations (e.g., governmental entities such as counties, fire departments, police departments, etc.). Such RF repeater systems permit a relatively limited number of RF communications channels to be shared by a large number of users--while providing relative privacy to any particular RF communication (conversation). Typical state-of-the-art RF repeater systems are "digitally trunked" and use digital signals conveyed over the RF channels (in conjunction with digital control elements connected in the system) to accomplish "trunking" (time-sharing) of the limited number of RF channels among a large number of users.
Briefly, such digitally trunked RF communications systems include a "control" RF channel and multiple "working" RF channels. The working channels are used to carry actual communications traffic (e.g., analog FM, digitized voice, digital data, etc.). The RF control channel is used to carry digital control signals between the repeater sites and user RF transceivers (radio units) in the field. When a user's transceiver is not actively engaged in a conversation, it monitors the control channel for "outbound" digital control messages directed to it. User depression of a push-to-talk (PTT) switch results in a digital channel request message requesting a working channel (and specifying one or a group of callees) to be transmitted "inbound" over the RF control channel to the repeater site. The repeater site (and associated trunking system) receives and processes the channel request message.
Assuming a working channel is available, the repeater site generates and transmits a responsive "outbound" channel assignment digital message over the RF control channel. This message temporarily assigns the available working channel for use by the requesting transceiver and other callee transceivers specified by the channel request message. The channel assignment message automatically directs the requesting (calling) transceiver and callee transceivers to the available RF working channel for a communications exchange.
When the communication terminates, the transceivers "release" the temporarily assigned working channel and return to monitoring the RF control channel. The working channel is thus available for reassignment to the same or different user transceivers via further messages conveyed over the RF control channel. An exemplary "single site" trunked RF repeater system is disclosed in commonly-assigned U.S. Pat. Nos. 4,905,302 and 4,903,321.
Single site trunked RF repeater systems may have an effective coverage area of tens of square miles. It is possible to provide one or more satellite receiving stations (and a single high power transmitting site) if a somewhat larger coverage area is desired. However, some governmental entities and other public service trunking system users may require an RF communications coverage area of hundreds of square miles. In order to provide such very large coverage areas, it is necessary to provide multiple RF repeater sites and to automatically coordinate all sites so that a radio transceiver located anywhere in the system coverage area may efficiently communicate in a trunked manner with other radio transceivers located anywhere in the system coverage area.
FIG. 1 is a schematic diagram of a simplified exemplary multiple-site trunked radio repeater system having three radio repeater (transmitting/receiving) sites S1, S2, and S3 providing communications to geographic areas A1, A2, and A3, respectively. Mobile or portable transceivers within area A1 transmit signals to and receive signals from site S1; transceivers within area A2 transmit signals to and receive signals transmitted by site S2; and transceivers within area A3 transmit signals to and receive signals transmitted by site S3. Each repeater site S1, S2, S3 includes a set of repeating transceivers operating on a control channel and plural RF working channels. Each site may typically have a central site controller (e.g., a digital computer) that acts as a central point for communications in the site, and is capable of functioning relatively autonomously if all participants of a call are located within its associated coverage area.
However, to enable communications from one area to another a switching network, as for example the assignee's "multisite switch" described herein, must be provided to establish audio and control signal pathways between repeaters of different sites. Moreover, such pathways must be set up at the beginning of each call and taken down at the end of each call. For example, the site controller (S1) receives a call from a mobile radio in A1 requesting a channel to communicate with a specific callee. A caller requests a channel simply by pressing the push-to-talk (PTT) button on his microphone. This informs the site controller S1 via an "inbound" digital control message transmitted over the RF control channel that a working or audio channel is requested. The site controller assigns a channel to the call and instructs the caller's radio unit to switch from the control channel to the audio channel assigned to the call. This assigned channel is applicable only within the area covered by the site.
In addition, the site controller sends the channel assignment to the multisite switch (200) which assigns an internal audio slot to the call. The multisite switch also sends a channel request over a control messaging bus to other site controllers having a designated callee within their site area. Audio signals are routed such that audio pathways are created to serve the callee(s) and one or more dispatcher consoles 202 involved in the communication. Upon receiving a channel request, these "secondary" site controllers (in the sense they did not originate the call) assign an RF working channel to the call. Each secondary channel is operative only in the area covered by the secondary site controller. The secondary site controller(s) also sends the channel assignment back up to the multisite switch.
Thus, the caller communicates with a unit or group in another area via the multisite switch. The call is initially transmitted to the primary site controller, routed through an assigned audio slot in the switch, and retransmitted by the secondary sites on various assigned channels in those other areas. When the call ends, the primary site controller deactivates the assigned channel for that site and notifies multisite switch 200 that the call is terminated. The multisite switch propagates an end of call command ("channel drop") to all other site controllers. This releases all working channels assigned to the call and breaks the associated audio routing pathways.
In addition to providing communications between mobile radio units in different areas, multisite switch 200 provides communications between land-line telephone subscribers and radio units as well as dispatchers and mobile radio units. Land-line telephone subscribers can communicate with radio units by dialing an access number as well as a radio unit (or group) identification number which is routed to the trunked communications system through a central telephone interconnect switch (CTIS) 212 and multisite switch 200. One or more dispatch consoles 202 is connected to the multisite switch in the same manner as the site controllers 102. Both land-line subscribers and dispatch console operators can issue a channel call request through the multisite switch to a site controller 102 to call for example a mobile radio unit.
Each dispatch console 202 may participate in calls in its area. Thus, when a call comes through the multisite switch from another area to a mobile radio, the switch informs the dispatch console 202 of the call in addition to notifying the corresponding site controller 102. The dispatch operator can then listen or participate in the call. Multisite switch 200 also handles calls to groups of mobile units and/or dispatch consoles by ensuring that the site controllers for all of the callees in the group assign a channel to the group call.
The multisite switch has a distributed control architecture. The logical functions and computational workload of the multisite switch are shared by various distributed microprocessor "nodes". Each node is connected either to a site controller 102, dispatch console 202, public and/or private landline telephone exchanges and other components of the particular communications system. Most nodes function as switch interfaces and include, for example, Master Interface Modules (MIMs) for nodes coupled to site controllers and Console Interface Modules (CIMs) for nodes coupled to dispatch consoles. Each interface module is supported by a controller card that utilizes several microprocessors. All of the cards have substantially the same hardware and are interchangeable. Each card acts as a gateway interface into the distributed control switch network.
Detailed description and operation of the multi-site switch, generally, is set forth in commonly assigned U.S. Pat. No. 5,200,954 entitled "Communication Link Between Multisite RF Trunked Network and an Intelligent Dispatcher Console", the disclosure of which is also incorporated herein by reference.
In general, trunked communications systems of the type described above operate independent of one another. Consequently, a user (or "communications unit") located in a first multisite communications system is not generally able to communicate with a second user located in a second multisite communications system. Thus, the overall coverage available to a user is limited to the particular coverage areas of a single multisite communications system. Recently, the assignee of the present invention overcame this limitation by providing fully trunked communication links between one or more multisite systems in a manner that is fast, flexible, compatible with existing multisite switch architecture and essentially transparent to users. In this regard, reference is made to U.S. patent application Ser. No. 08/156,785 filed on Nov. 24, 1993 entitled "Extended Trunked RF Communications System Networking," the disclosure of which is incorporated by reference.
More specifically, a dedicated Network Interface Module (NIM) provided in the multisite switch permits the interconnection and communication between multiple multisite switch controlled networks to create an extended overall communications network. The Network Interface Module allows a remote multisite switch controlled network to appear as just another node to the local multisite switch. Each network can then communicate over this common "node" interface permitting internetwork communication that is predominantly transparent to a network user. Moreover, using a plurality of network interface modules per switch, the overall communications network can be much extended by connecting individual multisite switch controlled networks together, for example, in series, "star" or multiple "star" configurations.
While single multisite systems provide console dispatch operations, console dispatch operations are not available in an extended multisite network. As a result, even though a local console in a local multisite network is programmed to monitor calls for a particular radio talk group, the local console is not able to perform basic and advanced console functions with radios in that talk group located in a remote multisite network. Instead, the console calls can only be handled like a typical radio call. For example, a console operator in an extended multisite network cannot select several talk groups and/or conventional (nontrunked) radio channels and patch them together as a single talk group over the extended network. In another example, a console dispatcher in a single multisite system may select several different entities including talk groups, individual radios, conventional radio channels, and/or wireline telephone numbers and communicate with them simultaneously, i.e., a "simulselect" feature. Like the extended multisite patch function, a console cannot perform a simulselect function outside of its local multisite network.
In addition, the present invention provides various console functions like "patch" and "simulselect" in an extended multisite RF trunked communications network in a fashion that is transparent to the console dispatcher. As a result, basic and advanced console dispatch functions may be performed by an operator in essentially the same fashion that those functions are performed in a single multisite radio communication system.
For example, when a local dispatch console requests a patch operation providing a list of specific entities to be patched at one of plural multisite systems, an available system assigned ID is selected and assigned to that patch list. The network interface module (NIM) local to that multisite system buffers the patch activation and transmits only those patches/simulselects that contain entities enabled for extended network communication. Accordingly, the local NIM does not interfere with the existing single multisite patch functionality. In addition, various entity IDs that are not enabled over the extended network may be reused in each individual multisite system.
The local NIM sends the patch message over a control link connecting a local multisite system with a remote multisite system where it is received by another network interface module (NIM) at the remote multisite, i.e., the remote NIM. Those entities at the remote multisite are programmed to the patch system assigned ID so that when a console dispatcher begins a substantive message from the local dispatch console, all entities in the local and remote multisites programmed with the corresponding patch ID will receive and can participate in the group communication set up by the dispatch console operator.
A state machine architecture is provided to implement console functions such as patch and simulselect over the extended multisite network. A timer is set for each state in the state machine to ensure smooth state transitions. Whenever a console operation does not proceed to the next expected state within the state timer interval, that operation is aborted. This is particularly advantageous in an extended multisite network where there are many different potential pit falls for a console function like a patch. The time limited state machine architecture helps ensure that all parts of the extended network affected by the console operation remain synchronized.
Current extended multisite networks also do not track which dispatch consoles in each multisite system are programmed to monitor specific entities, e.g., talk groups, conventional channels, etc., over the extended network. Even though a console remains in a constant location or "console position" (unlike portable radios), each console may monitor more than a hundred callees at one time over the extended network. Since many consoles throughout the different multisite networks may have the same callee selected/programmed, the problem is one of keeping track of the programmed state of each callee at each console over the extended network. This tracking problem is particularly complicated during dispatch operator shift changes, for example, where the programmed status of many callees may change in a very short time interval as new console dispatch operators log in with different programmed callee setups. Although one possible way of dealing with the tracking dilemma is to force all calls to any node that has a console to ensure that the console can monitor any of the calls, this method is inefficient because many calls which are not being monitored are nonetheless routed to that node.
In contrast, the present invention provides a console tracking procedure that allows more efficient use of the network channels in a system with consoles installed on multiple nodes. Calls are efficiently routed to remote multisite systems when the called entity (the "callee") is programmed by at least one console at the remote multisite system. Otherwise, calls are not routed to remote consoles. Using this technique, the extended network is not forced to route all calls to all consoles in every multisite system. Instead, the present invention only routes a call to multisite systems that have a console programmed to receive that particular call.
A console programmed entity database includes an entry in that database for each possible callee in the system. Each entry includes a count of local consoles at a particular local multisite system that currently have the callee programmed. When a console is programmed to add that callee, the count is incremented by one. Conversely, when a console having that callee programmed is reset or deprograms that particular callee, the count entry is decremented. If the count value for that callee reaches zero, then it is unnecessary for a call involving that callee to be routed to that particular multisite. The database also includes a list of callees currently programmed at each local console. Remote console data is stored for each callee indicating whether the callee is programmed at any console on remote multisite systems. Further tracking information is also stored for large internetworks of multisite systems, i.e., stargate connected multisite systems. Based on the information in this database, the local NIM decides which calls in its own local multisite switch need to be routed (through the local NIM) to consoles at remote multisites.